An Organic Electro-Luminescence Element (an Organic EL Element) is formed by an organic compound of fluorescence to be emitted through the addition of the electric field. A display device including a display panel having Organic Light emitting Diode (hereinafter referred to as an OLED) elements in each pixel is attracting attention as a next-generation display device.
This OLED is a current driving element and emits luminance in proportion to the flow of the current. The display device equipped with such OLED has drive transistors that are configured by the field-effect transistors (thin-film transistors) in each pixel, and controls current values of the current supplied to the OLED according to the voltage applied to the gates.
A capacitor is connected between the gate and the source in the drive transistor in each pixel, while the voltage corresponding to a video signal supplied from an external source is written into this capacitor in order to retain the voltage.
After the voltage is applied between the drain and the source, the drive transistor supplies the current to the OLED while controlling the current value at this gate voltage Vgs as the voltage Vgs (hereinafter referred to as a “gate voltage”) between the gate and the source.
The current value of the current to be supplied from the drive transistor to the OLED is determined according to the gate voltage Vgs value and the characteristics values of the applicable drive transistor (the threshold voltage Vth and the current gain β). The threshold voltage Vth is known to vary according to the past drive records in the pixel. When the variation in threshold voltage Vth occurs, the luminance of the OLED varies even if the gate voltage Vgs is the same, and consequently the quality of display image may be degraded.
Therefore, for the display device having light emitting elements such as the OLED in a pixel, the threshold voltage value Vth in each pixel is acquired, and the voltage value at the voltage to be applied between the gate and the source in the drive transistor is corrected according to the video signals based on the acquired threshold voltage value Vth. Therefore the development of the display device is pursued in order to improve quality display images.
However, as for an example of the current gain β, variations among the pixels may occur due to manufacturing processes. If the current gain β varies among the pixels, and even if the voltage value at the voltage to be applied between the gate and the source in the drive transistor is corrected after the threshold voltage Vth in each pixel is acquired, the degradation in display image quality caused by the variation of the current gain β among the pixels is not resolved.